Given
the potential shortage of critical nutrients (e.g., nitrogen,
phosphorus, and potassium) predicted in the near future, nutrient
recovery technologies have attracted wide attention from the scientific
community. In this study, a novel sequential double-column fluidized
bed homogeneous crystallization (SDC-FBHC) process was developed for
the simultaneous recovery of nitrogen (N), phosphorus (P), and potassium
(K) from actual swine wastewatera nutrient-rich source. Studied
variables included pH, reaction time, ammonia release, Mg:P ratios,
and up-flow velocity. Under conditions including pH 8.5–10.5,
a Mg:P ratio of 1.4, a P:K ratio of 1.25, an up-flow velocity of 30
m/h, and base on the initial N, P, and K concentrations of 515.6,
95.5, and 334.5 mg/L, respectively, the maximum total removal (TR%)
of N, P, and K reached 90.12%, 95.5%, and 62.7%, respectively, and
the crystallization ratios (CR%) were 85.6%, 92.4%, and 52.8%, respectively.
The sequential double-column fluidized bed homogeneous crystallization
products were composed of crystal magnesium ammonia phosphate (MAP,
MgNH4·PO4·6H2O, purity
> 71.1 ± 2%, size 1.0 mm) and magnesium potassium phosphate
phase
(MPP, MgKPO4·6H2O, purity > 67.7 ±
3%, size 0.95 mm), which are ready for use as a slow-release fertilizer.
The modeling of the minimum fluidization velocity resulted in values
of 1.4–1.8 and 1.6–2.0 times that of the up-flow velocity
for the effective fluidization of magnesium ammonia phosphate and
magnesium potassium phosphate, respectively. The estimated profit
for simultaneous recovery of N, P, and K from swine wastewater using
the sequential double-column fluidized bed homogeneous crystallization
process was 1.324 USD/m3-swine wastewater.